1. Technical Field
The present disclosure relates to a lighting device; more particularly, a lighting device for emitting twice-reflected light.
2. Description of Related Art
Recently, as the energy crisis attracts more and more attention, various innovative energy-saving lighting devices have been developed. Among them, the light-emitting diode (LED) is believed to be the next-generation lighting tool because of its advantageous characteristics of high luminescent efficiency, low power consumption, and mercury-free and long service life.
Regarding white light LED for illuminating purposes, the conventional technology has disclosed various manufacturing processes. Among them, some processes utilize the LED chip together with phosphors; for example, the blue light emitted from the blue-light LED chip excite the yellow phosphors to emit the yellow light, and then the blue and yellow lights are mixed to give the white light.
Common techniques for coating phosphors comprise a remote phosphor technique which coats the phosphor on a diffusion sheet. In comparison with conventional methods in which the phosphors are mixed with the sealant of the LED, the remote phosphor technique may prevent the phosphors from being affected by the heat generated from the irradiation of the LED chip. Moreover, since the service life of the phosphor is shorter than that of the LED chip, once the color temperature of the light changes, the user may simply replace the diffusion sheet and then the LED device can be still used. However, while coating the phosphor onto the diffusion sheet, because the coating area of the phosphor has to equal to the light output area, the usage of phosphor increases substantially. As the phosphors are quite costly, the manufacturing cost of the lighting device also increases.